1. Field of the Invention
The present invention relates to a device for creating a laminar flame front in an internal combustion-engined tool, in particular in a setting tool for setting fastening elements, including a combustion chamber with two walls extending parallel to each other and spaced from each other, with the device including an ignition element located between the two walls for igniting a combustible mixture located between the walls.
2. Description of the Prior Act
The internal combustion-engined tools, such as, e.g., setting tools for setting fastening elements, operate in accordance with Adams principle. In these tools, an ignition element is arranged between the two combustion chambers for igniting a combustible mixture, in particular an air-fuel gas mixture, an oxygen-fuel gas mixture or the like located between the two walls.
The two walls limit a fore-chamber, in which the ignition element is located, with one of the walls being provided with openings which communicate the fore-chamber with at least one further partial combustion chamber. When a further partial combustion chamber is present, it is designated as a main chamber and is adjoined by the operating piston of the setting tool. In each of the chambers, there is located an air-fuel gas mixture, possibly, with different mixing ratios. The combustion of the air-fuel gas mixture in the fore-chamber is initiated by an electrical spark produced by the ignition element, and a flame front spreads from the center of the fore-chamber, where the ignition element is usually located, with a relatively small speed, over the volume of the fore-chamber. The flame front pushes the unconsumable air-fuel gas mixture ahead of itself, and the unconsumable mixture flows, through the openings formed in one of the walls, into the adjacent further chamber creating there turbulence and pre-compression.
When the flame front propagates through the wall openings into the adjacent or main chamber, because of a small cross-section of the openings, it is accelerated and enters the adjacent chambers in a form of flame jets, creating there a further turbulence. The intermixed, due to the turbulence, air-fuel gas mixture is ignited over the entire surface of the flame jets. It burns with a high speed which results in a noticeable increase in the efficiency of the combustion, as the losses due to cooling remain small.
A drawback of the above-described process consists in that after the ignition of the air-fuel gas mixture in the fore-chamber, the formed laminar flame front spreads rather slowly. Therefore, the flame penetrates into the main chamber relatively late which reduces the efficiency of the combustion due to high cooling losses. Further, the initial pressure increase in the main chamber can result in a premature displacement of the piston though a complete ignition in the main chamber has not yet taken place.
Because of this, the air-fuel gas mixture in the main chamber becomes decompressed and is cooled off, which further reduces the efficiency of the combustion.
Accordingly, an object of the present invention is to provide a device which would permit to obtain a more rapid propagation of the flame front.
This and other objects of the present invention, which will become apparent hereinafter, are achieved by providing, between the combustion chamber walls, a cage for receiving the ignition element and which has, in an otherwise closed circumferential wall thereof, a plurality of openings extending parallel to the combustion chamber walls.
It has been found out that when the ignition element is surrounded by a cage, the spreading of the flame front after the ignition takes place only through the openings, which permits to obtain, already in the fore-chamber, a high flame spreading speed. Thereby, the flame penetrate into the main chamber more rapidly. This increases the combustion efficiency due to the smaller cooling losses. In addition, the observation has shown that the flame front after exiting the openings of the cage becomes again closed so that, it practically, reaches all of the openings in the combustion chamber wall which are equidistantly spaced from the ignition element, simultaneously.
Preferably, the openings, which are formed in the cylindrical wall of the cage, are equidistantly angularity spaced from each other. This provides for a symmetrical spreading of the flame front.
The cage itself can be formed as a hollow cylinder a longitudinal axis of which extends transverse to the combustion chamber walls. The cage forms part of a lug fixedly connected with one of the walls and sealingly extending through an opening formed in another of the walls.
The two combustion chamber walls can be made displaceable relative to each other and can lie on one another to provide for evacuation of the exhaust gas accumulated there between. Usually, both walls have a circular shape and are arranged coaxially with respect to the central longitudinal axis of the cage.
According to one embodiment of the present invention, the adjacent wall portions of the adjacent openings butt-join each other, forming common edges. This insures that the flame front, which propagates parallel to the combustion chamber walls, would never strike any portion of a cage wall that extends transverse to the spreading direction of the flame front. Thereby, a conversion of the flame front speed in an undesirable turbulence is prevented.
The novel features of the present invention, which are considered as characteristic for the invention, are set forth in the appended claims. The invention itself, however, both as to its construction and its mode of operation, together with additional advantages and objects thereof, will be best understood from the following detailed description of preferred embodiments, when read with reference to the accompanying drawings.